Memory is one type of integrated circuitry and is used in computer systems for storing data. Memory may be fabricated in one or more arrays of individual memory cells. Memory cells may be written to, or read from, using digitlines (which may also be referred to as bitlines, data lines, or sense lines) and access lines (which may also be referred to as wordlines). The digitlines may conductively interconnect memory cells along columns of the array, and the access lines may conductively interconnect memory cells along rows of the array. Each memory cell may be uniquely addressed through the combination of a digitline and an access line.
Memory cells may be volatile, semi-volatile, or non-volatile. Non-volatile memory cells can store data for extended periods of time in the absence of power. Non-volatile memory is conventionally specified to be memory having a retention time of at least about 10 years. Volatile memory dissipates and is therefore refreshed/rewritten to maintain data storage. Volatile memory may have a retention time of milliseconds or less. Regardless, memory cells are configured to retain or store memory in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
A capacitor is one type of electronic component that may be used in a memory cell. A capacitor has two electrical conductors separated by electrically insulating material. Energy as an electric field may be electrostatically stored within such material. Depending on composition of the insulator material, that stored field will be volatile or non-volatile. For example, a capacitor insulator material including only SiO2 will be volatile. One type of non-volatile capacitor is a ferroelectric capacitor which has ferroelectric material as at least part of the insulating material. Ferroelectric materials are characterized by having two stable polarized states and thereby can comprise programmable material of a capacitor and/or memory cell. The polarization state of the ferroelectric material can be changed by application of suitable programming voltages and remains after removal of the programming voltage (at least for a time). Each polarization state has a different charge-stored capacitance from the other, and which ideally can be used to write (i.e., store) and read a memory state without reversing the polarization state until such is desired to be reversed. Less desirable, in some memory having ferroelectric capacitors the act of reading the memory state can reverse the polarization. Accordingly, upon determining the polarization state, a re-write of the memory cell is conducted to put the memory cell into the pre-read state immediately after its determination. Regardless, a memory cell incorporating a ferroelectric capacitor ideally is non-volatile due to the bi-stable characteristics of the ferroelectric material that forms a part of the capacitor. Other programmable materials may be used as a capacitor insulator to render capacitors non-volatile.
The continual reduction in feature size places ever greater demands on the techniques used to form those features. One well-known technique is photolithography that is commonly used to pattern features, such as conductive lines or capacitor electrodes, on a substrate. The concept of pitch can be used to describe the size of these features. For a repeating pattern typical of memory or other arrays, pitch is defined as the distance between an identical point in two neighboring features. Adjacent features are typically separated by a material, such as an insulator. As a result, pitch can be viewed as the sum of the width of the feature and of the width of the space or material separating that feature from an immediately-neighboring feature. Due to optical factors, such as lens limitations and light or radiation wavelength, photolithographic techniques have minimum pitches below which a particular photolithographic technique cannot reliably form features. This minimum pitch is commonly referred to by a variable defining one half of the minimum pitch, or feature size F. This variable is often referred to as a “resolution.” The minimum pitch, 2 F, places a theoretical limit on feature size reduction.
Pitch multiplication (e.g. pitch doubling being one form thereof) is one method for extending the capabilities of photolithographic techniques beyond their minimum pitch, achieving a pitch of less than 2 F. Two pitch doubling techniques are illustrated and described in U.S. Pat. No. 5,328,810 to Lowrey et al. and in U.S. Pat. No. 7,115,525 to Abatchev, the disclosures of which are incorporated herein by reference in their entirety. Such techniques can successfully reduce the potential photolithographic pitch. Pitch multiplication can occur by other or greater than by “doubling”, including by non-integer values.
The invention was motivated in addressing issues associated with or arising out of pitch multiplication and photolithography, although it is not so limited.